The present invention relates to an optical wavelength multiplexing add/drop apparatus in which information to be received is separated from an optical wavelength multiplex signal including respective information allotted for a plurality of wavelengths and information to be transmitted in newly wavelength-multiplexed with such an optical wavelength multiplex signal, and further relates to an optical wavelength multiplexing communication system which includes an optical wavelength multiplexing network having a plurality of interconnected optical wavelength multiplexing add/drop apparatuses.
JP-A-63-272132 has disclosed an optical communication device in which information is separated from a wavelength multiplex signal and information is multiplexed with a wavelength multiplex signal. An example of the construction of such a conventional optical communication device is shown in FIG. 5. A wavelength multiplex input signal on an optical incoming line 81 is separated into optical signals of wavelengths .lambda..sub.1 to .lambda..sub.n-1 by an optical divider 82 and optical isolators 83. The optical signal of wavelength .lambda..sub.1 is separated as a reception signal by an element for wavelength .lambda..sub.1 in a wavelength converting element array 84. The remaining optical signals of wavelengths .lambda..sub.2 to .lambda..sub.n-1 are respectively wavelength-converted by the wavelength converting element array 84 into optical signals of wavelengths .lambda..sub.1 to .lambda..sub.n-2 as passing signals. Information to be transmitted from this optical communical device is carried by either one of the optical signals of wavelengths .lambda..sub.1 to .lambda..sub.n-1 is accordance with the position of an optical communication device to which that information is to be transmitted, and the information carrying signal is wavelength-multiplexed with the other passing signals by an optical multiplexer 85. The wavelength for the transmission signal is selected to be, for example, .lambda..sub.1 if an optical communication device to which that signal is to be transmitted, is the next or 1st optical communication device and .lambda..sub.2 if it is the 2nd optical communication device.
As a multi-stage optical switch circuit network for making a switching wavelength multiplex signals between a plurality of optical fibers, S. Suzuki et al "A Photonic Wavelength-Division Switching System using Tunable Laser Diode Filters" ICC'89, June 1989 has disclosed an optical switch circuit network in which wavelength converting switches are cascade-connected through wavelength separating circuits and wavelength multiplexing circuits. In the disclosed optical switch circuit network, wavelength converting switches for making a wavelength switching between wavelength multiplex signals to optical fibers are used as fundamental switches. At a first stage, a plurality of (or N) fundamental switches are provided in parallel and each of the outputs of the plurality of fundamental switches after wavelength conversion is separated into signals of discrete wavelengths by use of a wavelength separating circuit. Prior to the inputting of signals into the fundamental switches in a second stage, a combination of discrete output signal of different wavelengths from the respective fundamental switches in the first stage are collected with one wavelength being selected from each fundamental switch. These are multiplied by use of a wavelength multiplexing circuit to provide one wavelength multiplex signal. In parallel, another combination of discrete output signals of different wavelengths from the respective fundamental switches in the first stage are collected with another wavelength being selected from each fundamental switch and are multiplied by use of another wavelength multiplexing circuit to provide another wavelength multiplex signal. In this manner, the output signals in the first stage are multiplexed into N wavelength multiplex signals by use of N wavelength multiplexing circuits. These wavelength multiplex signals are wavelength-converted by N parallel-connected fundamental switches in the second stage, as in the first stage, and each of the outputs of the fundamental switches after wavelength conversion is separated into signals of discrete wavelengths by use of a wavelength separating circuit. Discrete output signals of different wavelengths from the respective fundamental switches in the second stage are multiplexed by N wavelength multiplexing circuits with different combinations each including one wavelength selected from each fundamental switch. These are thereafter wavelength-converted by fundamental switches in a third stage. A three-stage switch structure is formed by the above construction so that a large-scale switch is constructed by the combination of small-scale switches.